Hydrate Slurry Research Articles

Experimental study of methane hydrate formation and agglomeration in waxy oil-in-water emulsions

In deep-water multiphase flow pipelines, hydrate and wax agglomeration can cause blockages. To clarify the influence of wax and Tween 80 on hydrate formation and agglomeration in water-in-oil (W/O) emulsions, hydrate generation experiments were conducted in a high-pressure reactor, focusing on W/O emulsions both with and without wax and Tween 80. Additionally, the paper further explored the characteristics of hydrate formation and agglomeration in wax-containing W/O emulsions with Tween 80 under various initial pressure conditions. Results indicated that wax presence curtailed the Tween 80's dual role: inhibiting hydrate nucleation and promoting rapid hydrate growth. The interplay of waxes and Tween 80 had a synergistic impact on hydrate formation, elevating the cumulative gas consumption by 0.74 mol and augmenting the water conversion rate by 9 %. This intensifies the likelihood of hydrate blockages. Under higher initial pressures, a notable multi-step pressure decrease occurred during hydrate formation, attributed to a high water cut, wax/Tween 80 presence, and initial pressure. Torque evaluations indicate that wax-Tween 80 interactions diminish particle agglomeration, enhancing hydrate slurry liquidity.

Investigation of flow and viscosity characteristics of hydrate slurries within a visual-loop system

With the gradual advancement of oil and gas exploration into deep offshore, the hydrate blockage has emerged as a critical concern for the flow assurance. We conducted constant-velocity hydrate formation and variable-velocity rheology experiments with a novel visual-loop to analyze slurry flow and viscosity change in pipelines. Results showed staged pressure variations during hydrate formation-aggregation-deposition process, and it could be analyzed judiciously with a developed viscosity model. Initially, hydrates dispersed as small flocculent particles with minor aggregation, gradually raising differential pressure, and the critical viscosity model parameter, hydrate aggregation rate (m) was <1. Subsequently, particle aggregation and wall adhesion dominated, resulting in reduced hydrate flow volume and possible blockage of special pipelines (e.g., dead-leg), with m-values >1. Finally, as hydrate growth continued, substantial adhesion to the pipeline reduced flow diameter, significantly increasing blockage risk. However, the addition of sufficient surface-active ingredients improved hydrate dispersibility and enabled the slurry to maintain the first stage, exhibiting long-term stability with an m-value <1. Additionally, the apparent viscosity of the hydrate slurry within the pipeline was accurately determined utilizing a novel approach, accounting for its yield-pseudoplastic behavior. The calculated viscosities closely matched post-sampling rheometer measurements, and were effectively predicted by the developed viscosity model.

Correction to “Study on the Hydrocyclonic Separation of Natural Gas Hydrate Slurries Combined with the Solution of Particles’ Settling Equation”

Correction to “Study on the Hydrocyclonic Separation of Natural Gas Hydrate Slurries Combined with the Solution of Particles’ Settling Equation”

Numerical simulation of hydrate slurry flow behaviors with micron-sized sand in the transport pipe based on the population balance model

Numerical simulation of hydrate slurry flow behaviors with micron-sized sand in the transport pipe based on the population balance model

Analysis of CO2 hydrate formation from flue gas mixtures in a bubble column reactor

Gigascale carbon capture and sequestration (CCS) is increasingly seen as essential to meeting the targets of the Paris Agreement. As an alternative to conventional CCS approaches, carbon dioxide (CO2) hydrates have received attention as materials which can enable new approaches to carbon capture as well as carbon sequestration. CO2 hydrates (ice-like materials of CO2 and water) form at medium pressures (<400 psi) and temperatures of >0 °C from a water-CO2 mixture. Bubble column reactors (BCR) have been studied as a preferred way of forming CO2 hydrates. This study uses an inhouse, recently-developed modeling framework to predict performance of a BCR for CO2 hydrate formation from flue gas (CO2/N2), and pure CO2 streams. We highlight and analyze specific aspects of hydrate formation that are important for CO2 sequestration, and for CO2 separation/capture. In particular, two performance parameters are analyzed: i) gas consumption rate for hydrate formation (normalized with reactor volume), and ii) fraction of CO2 that converts to CO2 hydrates in a single pass (conversion factor). The first metric quantifies the overall productivity of a BCR by obtaining the net CO2 that can be sequestered or separated from the flue gas stream. The second metric relates to the efficiency of the system by quantifying the need for recirculation and the quality of the exit stream after a single pass. Extensive parametric analysis is conducted to study the influence of pressure, temperature, CO2 mole fraction at inlet, gas flow rate and reactor geometry on hydrate formation. Across the range of simulations conducted in this study, the highest gas consumption rate per unit reactor volume was 28.9 ton/yr/m3 and the highest conversion factor was 67.8 %. Both parameters increase with increasing pressure, decreasing temperature and increasing inlet mole fraction of CO2. Increasing gas flow rate increases the gas consumption rate (i.e., hydrate formation rate) but reduces the conversion factor. This suggests that the overall productivity of BCRs increases with gas flow rate at the expense of its efficiency. Reduced efficiency increases recirculation-related costs and high flow rate increases compression and cooling costs. For flue gas, increasing the reactor volume by increasing the height or diameter increases conversion factor but significantly reduces the gas consumption rate per unit reactor volume. For pure CO2, increasing the reactor height increases the conversion factor without changing the volumetric gas consumption rate. Decreasing the diameter increases volumetric gas consumption rate without changing the conversion factor. These findings suggest that compact reactors are more suitable for CO2 hydrate slurry production (on a volumetric basis), while larger reactors are suitable for CO2 separation/capture applications. Overall, this study provides a basis for the design and operation of BCRs for CO2 hydrates-based CCS applications.

Modelling Hydrate Deposition in Gas-Dominant Subsea Pipelines in Operating and Shutdown Scenarios

This study addresses a significant research gap related to hydrate formation in subsea gas pipelines, with a specific focus on deposition rates during shutdown scenarios, which has received limited attention in previous studies. Past research has employed various methodologies, including experimental, analytical, and computational fluid dynamics (CFD) approaches, to predict hydrate formation conditions, but none have tackled the prediction of hydrate deposition during shutdowns. In this study, we employ a multiple linear regression modeling approach using the MATLAB regression learner app. Four distinct regression models were developed using data generated from 81 CFD simulations, utilising a 10 m length by 0.0204 m diameter 3D horizontal pipe model in Ansys Fluent, as previously developed Through cross-validation against experimental data, the standard linear regression model emerged as the most reliable choice for predicting hydrate deposition rates, providing predictions within ±10% uncertainty bounds of experimental results up to pressures of 8.8 MPa at hydrate-forming temperatures. The uniqueness of this new model lies in its ability to estimate the risk of hydrate deposition in subsea gas pipelines, especially with low gas flow rates and during shutdown periods, which are critical for maintenance planning. Furthermore, by estimating depositional volumes, the model predicts hydrate slurry volumes at receiving facilities, contributing to energy sustainability and benefiting gas transport pipeline operators, particularly in aging gas fields with declining production.

Experimental monitoring of CO2 hydrate slurry crystallization by heat flux rate determination in a jacketed reactor

CO2 hydrate slurries are promising phase change materials for secondary refrigeration applications. However, the difficulty of experimentally evaluating the crystallization kinetic of slurries limits their industrial use. Hydrate crystallization kinetics monitoring performs traditionally by a reactor mass balance. However, this method requires assumptions on CO2 liquid phase concentration and the hydration number. This work outlines the development of a specific method to determine kinetics thanks to the direct measure of heat flow through the reactor jacket and its evaluation compared with the mass balance method. The results of each method are then obtained by testing the two kinetic parameters of stirring speed and propeller type. The final hydrate mass fractions obtained with both methods are in good agreement, but the kinetic obtained by the mass balance method is faster than by the heat balance method.

Simulation of the effect of hydrate adhesion properties on flow safety in solid fluidization exploitation

During the solid fluidization exploitation of marine natural gas hydrates, the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud. The potential flow safety issues arising during the transport process, such as the blockage of pipelines and equipment, have attracted considerable attention. This study aims to investigate the impact of hydrate adhesion features, including agglomeration, cohesion, and deposition, on the flow transport processes in solid fluidization exploitation and to provide a reference for the design and application of multiphase hydrate slurry transport in solid fluidization exploitation. We established a numerical simulation model that considers the hydrate adhesion properties using the coupled computational fluid dynamics and discrete element method (CFD-DEM) for the multiphase mixed transport in solid fluidization exploitation. An appropriate model to simulate the adhesion force of the hydrate particles and the corresponding parameter values were obtained. The conclusions obtained are as follows. Under the same operating conditions, a stationary bed is more likely to form in the transport process due to the hydrate adhesion forces; adhesion forces can increase the critical deposition velocity of the mixture of hydrate particles and cuttings. Hydrate adhesion lowers the height of the solid-phase moving bed, while the agglomeration and cohesion of particles can intensify the aggregation and deposition of hydrate debris and cuttings at the bottom of the pipe. These particles tend to form a deposit bed rather than a moving bed, which reduces the effective flow area of the pipeline and increases the risk of blockage.

Numerical simulation study on multiphase flow pattern of hydrate slurry

The research on the multiphase flow characteristics of hydrate slurry is the key to implementing the risk prevention and control technology of hydrate slurry in deep-water oil and gas mixed transportation system. This paper established a geometric model based on the high-pressure hydrate slurry experimental loop. The model was used to carry out simulation research on the flow characteristics of gas-liquid-solid three-phase flow. The specific research is as follows: Firstly, the effects of factors such as slurry flow velocity, hydrate particle density, hydrate particle size, and hydrate volume fraction on the stratified smooth flow were specifically studied. Orthogonal test obtained particle size has the most influence on the particle concentration distribution. The slurry flow velocity is gradually increased based on stratified smooth flow. Various flow patterns were observed and their characteristics were analyzed. Secondly, increasing the slurry velocity to 2 m/s could achieve the slurry flow pattern of partial hydrate in the pipeline transition from stratified smooth flow to wavy flow. When the flow rate increases to 3 m/s, a violent wave forms throughout the entire loop. Based on wave flow, as the velocity increased to 4 m/s, and the flow pattern changed to slug flow. When the particle concentration was below 10%, the increase of the concentration would aggravate the slug flow trend; if the particle concentration was above 10%, the increase of the concentration would weaken the slug flow trend, the increase of particle density and liquid viscosity would weaken the tendency of slug flow. The relationship between the pressure drop gradients of several different flow patterns is: slug flow > wave flow > stratified smooth flow.

An investigation on the variation of induction process in natural gas hydrate formation influenced by multiphase flow in a visual flow loop

One of the primary issues with natural gas transportation assurance is pipeline obstruction due to the formation and deposition of gas hydrates. Thus it is crucial to study the prevention and control methods of natural gas hydrateformation. A high-pressure visual flow loop was established in this study to investigate the effects of pressure, liquid velocity, and loop inclination angle on the formation of natural gas hydrates, hydrate slurry flow and morphology. For the formation of hydrates, it was demonstrated that the pressure was inversely related to the induction time and formation time. As the initial pressure increases, the conversion rate of water increases, leading to poor fluidity. With the increase of liquid velocity, the conversion rate of water increases and there is a threshold liquid velocity. Compared with horizontal loop, the hydrate particles in the slope were repeatedly deposited and removed off the surface of the sedimentary layer by gravity, and some large hydrate particles in the slope section gathered near the bottom of the pipeline. The induction time shortens and the formation time prolongs as the inclination angle increases. The inclination angle shows little effect on the final conversion rate of water, but it can delay the growth of hydrates obviously.

Experimental investigation to elucidate the hydrate Anti-Agglomerating characteristics of 2-Butoxyethanol

To alleviate the severity of hydrate formation in subsea oil and gas pipelines, the injection of anti-agglomerants (AAs) is one of the promising approaches. In this work, we investigate the hydrate anti-agglomerating characteristics of 2-butoxyethanol, also called butyl glycol ether (BGE), which has been reported in the literature as an effective synergist for kinetic hydrate inhibitors (KHIs), and a solvent for low dosage hydrate inhibitors (LDHIs). In view of its hydrophobic and hydrophilic moieties, we evaluate the adsorption affinity of BGE for the oil–water interface employing the interfacial tensiometer (IFT) apparatus. Moreover, a micromechanical force (MMF) apparatus was used to probe the interfacial behavior of hydrate particles, wherein we measured the cohesive forces between cyclopentane hydrate particles in the presence of BGE at atmospheric pressure and 274.2 K. The kinetics of methane hydrate formation and resistance-to-flow were assessed while measuring the dynamic pressure–temperature data and motor torque signals alongside with visual observations, respectively, employing a high-pressure visual autoclave (HPVA). IFT results reveal the strong surface active properties of BGE with a substantial reduction in oil–water interfacial tension at ambient conditions. However, no considerable change in the cohesive forces between cyclopentane hydrate particles was observed through MMF measurements. In contrast, HPVA results reveal that the addition of BGE enhanced the kinetics of methane hydrate formation; however, the corresponding torque pattern/visual interpretations indicated an anti-agglomerating action of BGE. While synergistically combining the BGE with under-inhibited dosages of mono-ethylene glycol, we further demonstrated a significant improvement in the hydrate transportability, wherein this synergism led to a non-plugging scenario (flowable hydrate slurry). Our findings will offer new insights into the development of new anti-agglomerant chemistries.

Investigation of the Behavior of Hydrate Slurry Flow in the Bend Based on the CFD-PBM Approach

Investigation of the Behavior of Hydrate Slurry Flow in the Bend Based on the CFD-PBM Approach

Gas Hydrate Formation and Slurry Flow Characteristics of Gas–Liquid–Solid Multiphase Systems

Hydrate formation, aggregation, and deposition have become major hazards for the safe transportation of oil and gas pipelines. Although there has been a great deal of research into the behavior of particles during hydrate formation and transport, there is less research into the multiphase generation and flow characteristics of hydrate gas and liquids. In this paper, the flow characteristics of hydrate slurry and the flow pattern transition in gas–liquid multiphase system were studied, and the generations of it were compared between a gas–liquid multiphase system and oil–water emulsion system. The results showed that the flow parameters such as pressure, pressure drop, and density fluctuated more drastically in the gas–liquid system than that in the emulsion system, the higher fluctuation meant a higher risk of pipe plugging. At the same time, the influence of pressure and dosage on multiphase flow pattern transformation and boundary change conditions were studied. A gas-slurry flow pattern transformation diagram was drawn based on the defined transformation conditions between flow patterns. The results also indicated that, with the increase of pressure from 5 to 6 MPa, the boundary of slug flow and air mass flow changed to the direction of higher gas and liquid flow velocity. While the boundary of slug flow and wave flow, stratified flow and wave flow changed to the direction of higher gas flow velocity. The boundary of slug flow and air mass flow changed to the direction of lower liquid flow velocity. In contrast, the boundary of slug flow and wave flow, stratified flow and wave flow, slug flow and stratified flow changed to the direction of higher gas flow velocity and lower liquid flow velocity in the 1% inhibitor period compared with that without the inhibitor. This study will provide theoretical references and technological supports for the safety of multiphase transportation pipelines and the safety of deep water production.

Rheology Properties of Cyclopentane Hydrate Slurry in the Presence of Wax Crystals

ABSTRACT There are several flow assurance problems for the energy development in deep-water, the coexistence of wax and hydrate resulting to multi-solid phase deposition is among the most difficult to overcome. The results of an experimental study on the effect of wax content, water cut, subcooling and static time on the CP hydrate-forming mixtures are reported. The droplet distribution at different wax contents is determined by using microscopic observation method. Using dynamic stress measurements method, a correlation between rheological properties and water cut is obtained. Hydrate nucleation, growth, dissociation, and slurry rheological properties, including critical time, growth time, final viscosity, and yield properties are determined. Results indicated that wax inhibit hydrate nucleation and growth, but the viscosity of hydrate slurry in waxy system is still higher than wax-free system due to the wax-hydrate aggregates contribute more to the viscosity of the system. The structure of hydrate slurry containing wax system is more stable and more difficult to be damaged by shear. Wax increases the hydrate slurry yield stress, and this effect is more significant at higher water cut and longer static times. The yield stress of the hydrate slurry was linearly related to the water cut. 35% was the critical water cut. Below the critical water cut, the slurry had better flow ability and less yield stress. Above the critical water cut, the yield stress increased significantly with water cut. The yield stress increased with increasing static time and decreases with increasing temperature. Nevertheless, the coupling effect of temperature with water cut and wax content was complex. Below 3 wt% wax content, temperature only has a significant effect on the yield stress of slurries with 40% and 50% water cut. Above 3 wt% wax content, temperature has a significant effect on the yield stress of all slurries with a 20–50% water cut. No ice formation in the CP hydrate-forming mixtures at −4°C, and the dissociation temperature of the hydrate decreases as the concentration of CP in the oil phase decreases.

Effect of cocoamidopropyl betaine on CH4 hydrate formation and agglomeration in waxy oil-water systems

Hydrates and waxes are the two major factors that provoke flow assurance issues in deep-water multi-phase transport units in the energy industry, and the application of eco-friendly and efficient anti-agglomerants is one of the key strategies for addressing this problem. The present work investigates the anti-aggregation performance of an environment-friendly amphoteric surfactant, Cocamidopropyl betaine (CAPB), in wax-containing oil-water systems. It is found that the anti-aggregation performance of CAPB in wax-containing oil-water systems is synergistically influenced by the concentration of CAPB and the wax content. The addition of 1.5 wt% CAPB can effectively inhibit hydrate formation and improve the flow of hydrate slurry in oil-water systems without wax. The addition of 2.0 wt% CAPB slows the growth rate of hydrates and reduces inter-particle aggregation in waxy oil-water systems containing 2.5 wt% n-Pentadecane. The wax content does not affect the amount of hydrate formation but influences the induction time and growth rate of hydrate formation. Additionally, the microscopic analysis further reveals that the addition of surfactant CAPB does not affect the crystal structure of hydrate, but has a significant influence on the distribution of methane molecules in the crystal cavities, particularly in wax-containing oil-water systems.

Assessment of flow pattern and rheological properties of SF6 hydrate slurry

Sulfur hexafluoride (SF6) has extremely high global warming potential and must be separated and recovered to avoid its emission into the atmosphere. Hydrate-based gas separation, which uses only water as the separation medium and has low environmental impact, is expected to become a new separation and recovery technology for SF6. However, this technique has the drawback that hydrate particles in the slurry can block equipment piping. Therefore, this study investigated the flow pattern and rheological properties of SF6 hydrate slurry using a loop-tube flow apparatus. SF6 hydrate slurry was observed to have three flow patterns as the flow velocity varied: homogeneous flow, heterogeneous flow, and moving-bed flow. We developed experimental relationships based on the Turian–Yuan equation to estimate the flow velocities at which the flow patterns change. These experimental equations were able to predict these velocities within an error of approximately 10%. The rheological properties of SF6 hydrate slurry were found to exhibit Newtonian tendency at low solid fractions and pseudoplastic tendency at high solid fractions. The relative viscosity of the slurry could be estimated within 25% error using the Krieger–Dougherty model.

Challenges and progress on ethane hydrates rheology under high pressure

One of the most common and critical inorganic deposition inside flowlines in the oil and gas industry is related to gas hydrates, which are crystalline water-based solids, formed in conditions of high pressure and low temperatures. In this work, experiments are carried out to analyze ethane gas hydrate formation in water-in-model oil emulsions, through a rheological analysis based on the variation of pressure, shear rate and water cut, using the vane and concentric cylinder geometries. High pressure time sweep tests were performed, and the results are presented through viscosity and pressure curves. The amount of water converted to hydrate was also estimated and related to the viscosity of the hydrate slurries formed. The results obtained show that the induction period was reduced by increasing the subcooling, water cut, and shear rate. Both geometries, vane and concentric cylinders, seem to be adequate to study hydrate formation and similar qualitative results were obtained, although the hydrate detectable and quantified region for the system employed were different.

Rheological properties of CO2 hydrate slurries in presence of Dioctyl sodium sulfosuccinate (AOT) in a dynamic loop for refrigeration application

Recent studies have shown real potential for using hydrate slurries as a secondary fluid in indirect refrigeration systems. However, pipeline clogging problems can appear due to hydrate agglomeration. Additives are generally used to counteract these problems. In this study, rheological properties of CO2 hydrate slurries in the presence of an additive Dioctyl sodium sulfosuccinate (AOT) are investigated. The capillary viscometer method is used to determine the fluid behaviour and the AOT impact on the slurry rheology. A dynamic loop is set up to collect experimental pressure drop and volume flow rate data. Based on the Rabinowitch and Mooney approach and Herschel-Bulkley model to determine the rheological properties, a shear-thinning behaviour was observed. The importance of the behaviour index choice in the procedure is discussed. Finally, the results obtained with AOT are compared with pre-existing studies. The present study highlights the AOT potential to significantly improve the CO2 hydrate slurries properties.

Natural gas hydrate formation and hydrate slurry transportation in a visual pipeline: reciprocal interaction, capacity prediction and potential regulation

Natural gas hydrate formation and hydrate slurry transportation in a visual pipeline: reciprocal interaction, capacity prediction and potential regulation

Study of hydrate slurry in dynamic systems: interaction between growth kinetics and flow patterns

Study of hydrate slurry in dynamic systems: interaction between growth kinetics and flow patterns